APPENDIX D
SAES-422
Multistate Research Activity
Accomplishment Report
Project Number: W-188
Project Title: Characterization of Flow and Transport Processes in Soils at
Different Scales
Period Covered: January 1 to December 31, 2000
Date of This Report: March 5, 2001
Annual Meeting Dates: January 3-5, 2001
Participants:
Arizona A.W. Warrick, Department of Soil, Water and Environmental Sciences, University of Arizona, Tucson, AZ 85721
P.J. Wierenga, Department of Soil, Water and Environmental Sciences, University of Arizona, Tucson, AZ 85721
California M. Ghodrati, Dept. of Env. Sci. Pol. Mang., University of California, Berkeley, CA 94720-3110
J.W. Hopmans, Dept. of LAWR, Hydrologic Science, University of California Davis, CA 95616
F. Leij, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
D.R. Nielsen, Dept. of LAWR, Hydrologic Science, University of California Davis, CA 95616
J. ?imùnek, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507-
T. Skaggs, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507-
M.Th. van Genuchten, George E. Brown, Jr. Salinity Lab - USDA-ARS, Riverside, CA 92507
L.Wu, Dept. of Envir. Sciences, University of California, Riverside, CA 92521
Yates, S. USDA-ARS, Riverside, CA
Meixner, T. University of California Riverside, Riverside, CA
Colorado G. Butters, Dept. of Agronomy, Colorado State University, Ft Collins, CO 80523
Delaware Y. Jin, Dept. of Plant and Soil Sciences, University of Delaware, Newark, DE 10717-1303
Idaho J. B. Sisson, EG&G, Idaho National Engin. Lab., Idaho Falls, ID 83415-2107
Illinois T.R. Ellsworth, University of Illinois, Urbana, IL 61801
Kansas G. Kluitenberg, Dept. of Agronomy, Kansas State University, Manhattan, KS 66506
Montana J. M. Wraith, Land Resources and Environ. Sciences, Montana State University, Bozeman, MT 59717-3120
Nevada S.W. Tyler, Hydrologic Sciences Graduate Program, University of Nevada, Reno, NV 89532
Utah D. Or, Dept. of Plants, Soils & Biomet., Utah State University, Logan, UT 84322
Washington M. Flury, Dept. of Crop & Soil Sciences, Washington State University, Pullman, WA 99164
Wyoming R. Zhang, Dept. of Renewable Resources, University of Wyoming, Laramie, WY 82071
CSREES R. Knighton, USAD-CSREES, Washington, DC 20250-2200
Adm. Adv. G.A. Mitchell, Palmer Research Center, 533 E. Fireweed, Palmer, AK 99645
Minutes of the Annual Meeting: The minutes of the annual meeting may be found on the W-188 web site at: lsci. n dsu.nodak.edu/w188
Accomplishments and Impacts:
Objective 1: To study relationships between flow and transport properties or processes and the spatial and temporal scales at which these are observed
Accomplishments:
CA-Berkeley and other W-188 participants addressed the question of temporal changes in solute transport processes in field soils and posed the question of whether calibrating a flow model for a single time period was adequate. Using fiber optic miniprobes (FOMPs) and time domain refelectometry (TDR) in a field soil they found indications that solute transport converged into fewer pathways over time with repeated leaching and that transport response patterns are not temporally stable.
Researchers in IA responding to national concerns of potential soil and groundwater contamination by polycyclic aromatic hydrocarbons (PAHs) investigated how sorption kinetics may affect the fate and movement of these compounds in the soil profile. In studies with naphthalene they found that increasing ionic strength influenced the degree of aggregation, enhanced the sorption affinity and retarded the transport of naphthalene. These findings are important for both risk assessment and remediation of contaminated soils and aquifers.
Other IA research on diffusivity in rock matrices as affected by temporal and spatial scale, determined that applying diffusivity measurements from laboratory samples to a large rock formation would grossly over-estimate the diffusive mass transfer.
Investigators in KS studied temporal stability of corn yield patterns in three locations over periods > five years. Their findings suggested that temporal stability is relatively weak and that long-term yield monitoring (> 5 years) may not be useful in determining persistent yield patterns.
Infiltration experiments in field soils in ND investigated relationships between water transfer and solute transport in soils exhibiting preferential flow. Using TDR probes, they found that water content continued to increase after steady flow rate was reached, indicating that water was being transferred from rapidly filling, highly conductive pores to slower filling less conductive pores.
On-going research by CA-USSL (ARS) involved further improvement of the HYDRUS-1D and HYDRUS-2D window-based software for rapid estimation of hydraulic input parameters for specific applications. For example, it is a more effective method for estimating unsaturated soil hydraulic properties and HYDRUS codes have been applied to a large number of agricultural problems. These include infiltration, tile drainage, crop production, and fate and transport of agricultural chemicals. Other applications are possible in the general area of soil and groundwater pollution.
CA-USSL used percolation cluster statistics and critical path analysis to derive an analytical expression for the expected value of the hydraulic conductivity as a function of system size. Also. CA-USSL and CA-Riverside measured 0-6 cm soil water content on consecutive afternoons at four hundred locations in a gently sloping range field. Spatio-temporal data analyses of the two sampling events showed a change in field variance suggesting moisture was redistributed by base flow, evapotranspiration, and condensation. The largest contributor to variability was relative landscape position.
CA-Riverside pursued investigations related to unstable flow on fields chosen because they were favorable to preferential flow during moisture redistribution. A third CA-R project studied atmospheric deposition of ammonia or oxides of N on downwind terrestrial and aquatic ecosystems and the influence of deposition, nitrate production rates, stream source waters and processes, and catchment properties on stream NO3- levels.
SAES researchers in WA studied the relationship between flow and transport properties and their spatial and temporal scales in relation to remediation of uranium contaminated mine waste, viral transport in unsaturated porous media, and erosion processes in agricultural soils under unique climatic conditions. They also determined reaction rate coefficients of uranium sorption/precipitation and evaluated the use of apatite as a leaching barrier. Apatite proved to be very effective at removing uranium from solution. WA and DE collaborated on a model to describe virus movement related to solid-liquid and liquid-gas interfaces. They concluded that in the presence of solid surfaces, reactions at the solid-water interface, rather than the air-water, dominated in virus removal and transport under unsaturated conditions. These studies, while reflecting very fundamental science, have obvious implications for applied use in minimizing soil and groundwater contamination by a range of chemical and biological pollutants.
Nitrogen and P transport in desert and alpine watersheds were studied by NV scientists. They found surprisingly high levels of nitrate accumulation (>5000 mg/l) below the root zone in desert soils of southern Nevada. They determined the source to be atmospheric deposition and N fixation from soil microbial crusts and that contrary to previous views, N availability was not a limiting factor in ecosystem response but correlated more with water availability.
Impacts:
The W-188 technical committee research addresses fundamental soil physical processes related to water and solute transport across a range of spatial and temporal scales. Impact on stakeholders is not direct in most cases. However, collaborative research will provide new information that vastly improves our understanding of how to interpret measurements and process studies so their information content can be transferred to the larger domain of practical application. The latter will include other land grant scientists, extension specialists, state and federal agency scientists, and the private sector.
Objective 2: To develop and evaluate instrumentation and methods of analysis for characterization of flow and transport at different scales .
Accomplishments:
The natural heterogeneity in water and solute movement in hillslope soils makes it difficult to characterize the transport of surface applied pollutants without obtaining spatially distributed hydrologic data. CA-Berkeley scientists developed methodologies utilizing in situ portable time domain reflectometry (TDR) to measure solute transport on hillslopes. The TDR system was shown to be an effective means to characterize solute travel times on hillslope soils. CA-Davis investigated interdependence of soil strength on water content. They found field water content changes both spatially and temporally, limiting the application of cone-type penetrometers as an estimate of soil strength. They have developed a combined coiled penetrometer and moisture probe to study water content effects on soil strength. CA-Davis and CA-USSL collaborated to develop inverse modeling methods to estimate soil hydraulic properties. Successful application of the inverse modeling technique improves both speed and accuracy since there is no need to attain steady-state flow.
Researchers at IA are investigating soil thermal properties as a function of soil volume fractions. They found that thermal properties were most closely correlated with the volume fraction of air, heat capacity, and thermal conductivity. The strong relationship with porosity had not been previously reported and will be useful for improved thermal modeling. In other research, IA developed and evaluated methodology that would allow rapid field measurement of soil hydraulic and transport properties with minimal labor requirements.
Kansas researchers continued development of new methodology for measuring soil water flux density using a heat tracer to quantify the magnitude of convective heat transfer resulting from soil water movement. The downside of the methodology involved lengthy evaluations of integrals. Collaboration with AZ in 2000 focused on reducing the integrals in the solutions to the well function for leaky aquifers. Their approach resulted in being able to evaluate the function with excellent accuracy by using only 0, 1 or 2 terms in most cases. Other KS research utilized the dual-probe heat-pulse (DPHP) method for measuring soil volumetric water content.
Montana and UT collaborated on using the concept calibrated reference soils with known water retention characteristics as a means to estimate the unknown retention characteristics of soils in situ. They used TDR probes embedded in target and adjacent reference materials. Results indicate the ability to capture continuous paired water content measures over the entire wetness range may provide more accurate values than using pressure steps alone.
Montana assisted the U.S. Department of Energy in evaluating potential efficacy of a proposed unsaturated flow encapsulation system. A block of soil activated around a proton beam target assembly had resulted in creation of radioactive isotopes of naturally occurring elements including tritium and sodium 22. They proposed injecting a low viscosity colloidal silica grout (CS) to fill void space to encapsulate the activation-zone soils. Early laboratory simulations look very promising.
Other methodologies in various stages of development under Objective 2 included:
· CA-Riverside and USSL developed a new method to directly measure the porosity and its microscopic characteristics.
· CA-Riverside evaluated methods for measuring Oxygen Diffusion Rate (ODR)for the soil matric potential range of 0 to 40 kPa using a platinum electrode in conjunction with TDR and tensiometer probes. The application of the technology indicated that comparison of air-filled porosities alone in different soils has little meaning relative to root growth.
· Utah developed a method for predicting unsaturated hydraulic conductivity functions based on pore scale hydrodynamics of flowing films and flow in corners bounded by liquid vapor interfaces.
· WA scientists developed an experimental and theoretical methodology to determine the moisture characteristics from freezing experiments.
· Arizona conducted a flow and transport experiment with bromide tracer at the Apache Leap Research Site. They used backup monitoring by neutron probe, tensiometers, and suction lysimeters in addition to the tracer. They found transport of bromide to some deeper depths in a relatively short time and the bypass of bromide at many shallower depths is clear evidence of fracture flow not picked up by water content and tension data.
· Nevada and CA-USSL studied flow and transport processes for arsenic through gold mining wastes in southern Nevada. They found pH changes in response to pyrite dissolution reduced arsenic mobility but the shifts in redox counterbalanced the pH change. They concluded that elevated levels of arsenic I drainage water would continue at these sites for significant time (>100 years).
Impacts:
W-188 scientists have developed a variety of soil physical instruments and corresponding methodologies that substantially advance theirs and other soil and water scientist’s capabilities to gain new insights into soil physical parameters at laboratory and field scale. Agricultural and environmental disciplines beyond soil physics will also benefit both by the discoveries reported here as well as their own discoveries utilizing instrumentation, theory, and models produced by this committee.
Objective 3: To apply scale-appropriate methodologies for the management of soil and water resources.
A four-year IA study used a paired watershed approach to evaluate optimum fertilizer N in a soybean-field corn rotation on 8 farms and studied resulting effects on water quality in tile drainage. Using the late spring nitrogen test (LSNT) for N application recommendations, they documented a 41 % reduction in nitrate-N in tile drainage water compared to the control watershed. This was the first documentation of the impact of an LSNT program on water quality at a spatial scale that is environmentally meaningful. Other N research found that nitrate concentrations in tile-drain water exceeded the USEPA maximum contaminant level (MCL) when cropped with corn at all N application levels tested (67 to 202 kg N/ha). In other words, their findings suggested that economic corn production cannot be sustained in those fields with current corn-soybean management without producing drainage water that exceeds the MCL for nitrate.
Mapping soil water content for site-specific management of farm fields is commonly achieved through time consuming and destructive core sampling. Montana researchers designed and built a heavy duty TDM probe that is accommodated by a hydraulic soil sampling machine. Utility of the probe to assist in developing kriged field scale soil water maps was demonstrated in several production agricultural fields. Additionally, MT established two 70-acre on-farm study locations with 80 neutron probe access tubes for detailed water content monitoring. This data was combined with automated climate data for continuously updated water content status and crop yield estimates. This was interfaced with GIS programs currently being used by producers for eventual use in remote sensing to infer progression of crop water deficit.
Other accomplishments under this objective included:
· Montana scientists completed a study to evaluate the impact of spotted knapweed on soil physical properties, soil hydraulic properties, soil water status, and near surface thermal properties. They determined that reports of soil degradation by spotted knapweed was primarily anecdotal.